Psa 144:3 O LORD, what is man that thou dost regard him, or the son of man that thou dost think of him?
There's only one answer here - love. God could have abandoned us after the Fall. Or God could have simply not created us. He could let us meander about on Earth, sinning against Him and earning eternal damnation with Satan. He could wipe the planet out of the universe, like it never existed. Instead, He he loves us. He loves us so much he sent Jesus to save us. Isn't that awesome?
Joh 3:16 For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life.